ASME max. allowable bolt stress 50% Sy ?

[cornemo]

Dear all,

I'm doing a calculation for a modified flange according to ASME VIII div 2 at 310 bar and 300 degr. C (with PVElite for those that are interested). The bolt material used is the European 34CrNiMo6 (acc. EN-10269).

What I've done is the following.
- I've modelled the flange as in the design drawing.
- Then I made a max. allowables table for the material myself as the program doesn't recognize this material as allowable in an ASME calculation.
- My first problem is that no properties at high temperature are given for this material in EN-10269. I've now taken the values from PVElite EN-13445 calculation tables.
- Secondly I checked the flange and it had not enough bolt area.
- My client said to use 50% of Syt as allowable for the bolts. I however can't find a reference for this in ASME VIII nor in ASME II. I know there is appendix S which refers to higher bolt stresses during assembly. But if I make a design calculation bolt stresses should be below allowable I think.

So 2 actual questions:
- Where can I find the allowables, Yield at temperature values for 34CrNiMo6 in EN-codes for bolting materials?
- Where can I find that during an ASME flange design the bolt stress may reach to 50% of Syt?

Thanks in advance for your replies.
With regards,
Corné

 

[TGS4]

You need to DESIGN your flange using the ALLOWABLE bolt stresses, not the ones that will actually be used in service. Then, go ahead and use whatever bolt load you want after. I would tell my client to reference PCC-1 for bolt stresses. 50% of yield actually sounds a little low...

I know this sounds little "off", but this is exactly what Appendix S tell you to do.

 

[cornemo]

I know that, but in design conditions my client already tells me to use 50% of Syt to use instead of the maximum allowable stresses. He says this is incorporated in the codes somewhere. He can't tell me where exactly and I can't find it.

 

[TGS4]

That's between your client and you. It's definitely not in the Code.

 

[cornemo]

I already had that idea that it's not in the code.
So what I do is calculate the forces and bending moments in the flange. These forces are then divided by the number and area of the bolts and these stresses are checked towards the allowables.

Can you also answer my other question about allowables of 34CrNiMo6 which are not given in EN-10269?

 

[TGS4]

Sorry - can't help you with the allowable issue. Not my specialty.

 

[rmw]

You don't have an ASME material so if I were in your situation, I would look at ASME acceptable bolt materials, determine the various tensile strengths of those materials, and then take the ASME allow-ables and establish a ratio. I would then apply that ratio to the material that you want to use and see if your governing authority will accept that approach. ASME allow-ables are very (make that VERY) conservative and that is the end goal of the code, to have the flange designed with conservative values.

See if you can sell that to both your client and your (or his/her) governing authority. In the end, it is whoever it is that is going to certify the vessel that has to be satisfied, not your boss, or the client.

Another approach I might use is to design it with ASME acceptable bolting materials and then use what you want that meets or exceeds the ASME material, but only if this flange is on a nozzle, and not part of the vessel body (pressure boundary) itself. If it is a nozzle flange, the code doesn't govern that bolting, rather the appropriate piping code. If the nozzle is blinded, then the blind is part of the pressure boundary and governed by the code.

Third tip: you may want to go post this question over in the ASME Forum, but ask it differently, don't double post.

rmw

 

[rneill]

I just wanted to reinforce TGS4's posts - he is right on the mark.

Not 100% sure about ASME Section II but para 302.3.2 of B31.3 specifies the criteria by which the design allowable stress values for bolting published in Table A-2 of B31.3 are derived. I assume that similar criteria are published in BPVC (e.g., Section II) as well - they may in fact be the exact same criteria but I'm not sure.